'00 V70 FWD: Fuse 27 keeps blowing - reverse lights / turn signal Topic is solved

[brooklynsystems]

Hey Everyone- long time user here- hardly ever need to post! I'm having an issue where I'm blowing fuse #27 (Turn Signal / reverse light). After I replace the fuse it works for a few minutes then blows again. Hazards work fine, turn signals seem to work fine. Reverse lights don't work even when the fuse is not blown. The reverse bulbs are fine, the wiring looks going into them looks fine. I'm not getting voltage back there when reverse is engaged. I'm thinking maybe the PNP switch is the culprit, but if it's the PNP, could that cause a blown fuse? Any guidance would be much appreciated.

[Clemens]

well, if the reverse light switch (which is probbaly somewhere down by the shifter assembly/pnp switch) shorts out, it could cause the fuse to blow. this would also explain the no voltage at the reverse lights

[BEJinFbk]

Was the car ever set up to tow?

[abscate]

The V70’series often has trouble in the wiring loom in the left tailgate strut.

The wires break inside the loom and short out. There are some detailed threads on this here

[brooklynsystems]

Thanks folks! The reverse lights are controlled by PNP switch, right? I don't think the car was set up to tow. I don't see any splices or piggybacks in there. I don't think in my V70 wagon that the reverse lights are in the tailgate door (the lights are on the body) so I don't think it's in the strut wiring loom, right?

Weird thing happened this afternoon where the turn signals work in Park only, but then in reverse, neutral, drive they don't work.
It hasn't completely burned the fuse yet. Reverse lights still not working at all.

[SuperHerman]

You need to get a volt ohm meter (VOM) and check for shorts. If you have a short you need to find it and fix it.

If you keep driving the car with the issue you could ruin the wire loom and possibly burn your car.

If you cannot find any shorts - pull the wire diagram and check the relay and shunt that are part of that circuit.

[brooklynsystems]

I could use some help in diagnosing this. I've watched so many videos on finding a short, but still a bit confused. Here's what I can tell you: with fuse (#27) removed, VOM set to DC volts, I'm probing the load side of the (#27) fuse socket to battery + and getting 12.5V. That means there is a short, yes? Also on the line side of fuse socket to battery+ it's reading 12.0V. Does that mean there is a short to ground between the battery and the fuse box? So where do I go from here?
Other facts:
car runs fine, everything works except turn signal and reverse lights
Hazard lights work
Turn signals work in park even with a blown fuse (they don't work in reverse, neutral or in forward gears)
when I replace the fuse the reverse lights work (in reverse) for about 10 seconds before the fuse blows.

Any help with this would be much appreciated!

[SuperHerman]

For finding a short one uses the Ohm scale on the VOM. One lead goes to a known ground point on the car, the other to the wire being checked. I would unhook the battery and let it sit for a bit - maybe cross the two cables to discharge the system. You can use the voltage scale to figure your power line and ground line.

Any wire that is grounded will show no resistance. Some wires will show very little resistance, but you will have to look at the wiring diagram to see if this is acceptable. In most cases one side will be the ground wire and the other the power feed. Power feed should never show any resistance or extremely little (again depends what one is checking). If a power feed line is grounding out then that is your problem - you have a short circuit.

I would isolate your circuit and check the relays and shunts - as stated in the past, I had a 2002 XC70 that kept blowing the same fuse and it ended up being a bad shunt on the CEM. I ripped the car apart looking for my short. At one point, as I recall there were three shunts - I pulled them all out and didn't mark them. I managed to put the bad shunt back into the same circuit - pure chance (and stupidity on my part for not marking it). As it kept blowing the fuse I moved on thinking I swapped places. In the end I cam back and found my problem - this was after a CEM rebuild, a new used climate module and countless hours. You can swap shunts of same part number to test. Just mark the shunt that handles the circuit for the lights at issue clearly with nail polish, tape or what ever. Don't plug it in to the swapped out shunt socket. Expect errors to occur where you pulled the donor shunt as that circuit will be out. By the way I have no idea how to test a shunt - I looked and never figured out how.

[BEJinFbk]

Good News - Your car doesn't have any relays or shunts
between the PNP switch and the reverse lamps. The 2000
70 series cars were pretty simple and don't have any goofy
stuff like a Central Electric Module. You turn the key, the relay
that provides power to accessories ( 2/6 ) energizes and makes
power available at the supply side of Fuse 27. From there, it
goes through the PNP switch and back to the lamps. The
lamps ground in back.

You can see all of this in the wiring diagram. The digram covers
the Sedan, Coupe and wagon variations, just trace the path called
out for the V70 and remember that you have a Left Hand Drive car.

The Component Locations PDF will show you where all of the parts
are located and grounded. BTW - Be sure to check the grounds in back!
If they're loose, a lot of strange things can happen.

You might try unplugging the PNP, removing both reverse lamps and
checking for continuity ( in the OHM X1 setting ) between the wire leaving
the PNP to the lamps to ground. It should be a blue wire on pin 5 of the
PNP connector. You an go right to the battery (-) connection for ground.

With the lamps removed, the meter should see no connection to ground.
The reading on the meter shouldn't change at all. ( When the lamps are in,
you'll see ground through the lamp filaments, because at the end of the day,
the filaments are just pieces of wire, and they connect to ground).

Here are a couple of things to help you check this all out.

TP3938202 C70 S70 V70 1999 Reverse Light Wiring Diagram.pdf

(169.48 KiB) Downloaded 39 times

TP3938202 C70 S70 V70 1999 Reverse Light Component Locations.pdf

(235.44 KiB) Downloaded 12 times

.
One other thought - Is the stereo still stock?
Any chance someone had an HU with a backup cam?

[brooklynsystems]

Thank you guys much! Good info that I needed. Glad to hear that I don't have a CEM or shunts! I was starting to worry that there were parts of my car I never knew existed...
I'll take a look tomorrow.
Stereo is stock.